Hi - I have been photographing everything I can that lives in ponds and I found two types of hydra. I have photographed the hydra feeding on copepods and Daphnia - though they seem to leave Ostracods alone. Also included some high mag photos of the 4 types of cnidoblasts.

I used a combination of low power to capture the entire Hydra using 2.5, 5X objectives and high power 40X, 63X objectives with DIC to capture the cnidoblasts. Below are some pictures - if you are interested in learning more about Hydra - see the article I just posted. http://www.canadiannaturephotographer.com/hydra.html - I have included links to PDFs of various research papers and online books.